Backport metal implementation to jfx25u. The backport is nearly clean with only one conflict that: The file `modules/javafx.graphics/src/main/java/com/sun/glass/ui/headless/HeadlessView.java` is not present in jfx25u. No issues observed with build and test.
------------- Commit messages: - 8271024: Implement macOS Metal Rendering Pipeline Changes: https://git.openjdk.org/jfx25u/pull/30/files Webrev: https://webrevs.openjdk.org/?repo=jfx25u&pr=30&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8271024 Stats: 12322 lines in 105 files changed: 11457 ins; 709 del; 156 mod Patch: https://git.openjdk.org/jfx25u/pull/30.diff Fetch: git fetch https://git.openjdk.org/jfx25u.git pull/30/head:pull/30 PR: https://git.openjdk.org/jfx25u/pull/30
